The optical membrane is one of important materials for manufacturing a liquid crystal display (LCD) device. A conventional optical membrane is poor in stiffness, and thus is prone to be deformed and wrinkled upon being heated by hot air. For example, a light strip of the backlight module may generate a considerable amount of heat, and thus it is very likely that the optical membrane of the backlight module is heated by the hot air around the light strip and wrinkled. As illustrated in FIG. 4, the optical membrane 401 is wrinkled to have wrinkle 402 due to being heated by light emitting diodes (LEDs) 403, which adversely impacts quality of the backlight module and display quality of the LCD.